The invention relates to a method and a device for checking a marking element for shift or displacement in relation to a holding structure, in particular a bone, on which this marking element is fixed, said marking element being used for determining position in navigational surgery.
In navigational surgery (computer-assisted surgery), robots are used in order, for example, to ream out bone cavities or to make incisions in bone or to saw through bone. By this means, the site of the reaming or the site of the incision can be set with precision. To do so, however, it is necessary that the spatial positions of the machining tools relative to the operating field are known at each point in time with a high degree of accuracy.
For this purpose, marking elements are used which are fixed on a corresponding holding structure or on various holding structures. The marking elements are fixed in particular by using bone screws which are fixed on a corresponding bone. In a hip operation, for example, one or more marking elements are fixed on the corresponding hip bone. When fitting a knee prosthesis, marking elements are fixed on the bones of the foot, on the bones of the lower leg, on the femoral bone, and on the hip bone.
Assuming that the marking elements are fixed securely on the holding structure, a navigation system can be used to determine their spatial position and thus in turn to control the machining tool.
With the present invention, a simple method and a simple apparatus for checking a marking element for displacement in relation to the holding structure is made available, said marking element functioning with the greatest possible precision.